This invention relates to implantable medical devices which monitor the cardiac state of a patient by sensing sinus rhythm, ventricular tachycardia and ventricular fibrillation and which deliver therapy in the form of electrical energy to cardiac tissue in an attempt to revert tachycardia and restore a normal sinus rhythm.
As used herein, antitachycardia pacing will mean any pacing for the reversion of tachycardia. The term tachycardia refers to any fast, abnormal rhythm of the heart which may be amendable to treatment by electrical discharges and specifically includes ventricular tachycardia (VT), supraventricular tachycardia (SVT), ventricular flutter and/or ventricular fibrillation (VF).
The term therapy as used herein includes the processes used between the detection and reversion of a tachyarrhythmia and includes the actions of antitachycardia pacing, cardioversion and/or defibrillation shocks. The term cardioversion refers to the discharge of electrical energy into the cardiac tissue in an attempt to terminate or revert a tachyarrhythmia. This may take the form of a high energy discharge (up to 40 Joules or more) or a low energy discharge (less than 1 Joule). Cardioversion shocks may or may not be synchronized to the rhythm of the heart. Defibrillation is a particular example of cardioversion.
This invention applies equally to devices which deliver energy synchronized to an R-wave and to those that do not. It also applies to devices which use lower energy pulses (up to 1 Joule) as well as to devices which use higher energy pulses (up to 40 Joules or more). The invention applies to devices which deliver cardioverting shocks alone as well as to devices which deliver antitachycardia pacing pulses alone or in combination with cardioverting shocks. The invention will usually apply to ventricular implantable cardioverters, but is equally applicable to atrial cardioverters or multiple chamber cardioverters or defibrillators. The invention applies also to the delivery of any antitachycardia pacing pulse and post reversion pacing therapy.